In general, as shown in FIG. 1, an air conditioning system for a vehicle has a refrigeration cycle that includes: a compressor 1 for compressing and discharging refrigerant; a condenser 2 for condensing the refrigerant of high pressure discharged from the compressor 1; an expansion valve 3 for throttling the refrigerant condensed and liquefied in the condenser 2; and an evaporator 4 for exchanging heat between the liquefied refrigerant of low pressure throttled by the expansion valve 3 and air blown to the interior of the vehicle and for evaporating the refrigerant to cool the air discharged to the interior of the vehicle through heat absorption by evaporative latent heat, and that the compressor 1, the condenser 2, the expansion valve 3 and the evaporator 4 are connected with one another via refrigeration pipes. The air conditioning system cools the interior of the vehicle through the following refrigerant circulation process.
When a cooling switch (not shown) of the air conditioning system is turned on, first, the compressor 1 inhales and compresses vapor-phase refrigerant of low-temperature and low-pressure while driving by driving power of an engine or a motor, and then sends the refrigerant in the gaseous phase of high-temperature and high-pressure to the condenser 2. Then, the condenser 2 condenses the vapor-phase refrigerant into liquid-phase refrigerant of high-temperature and high-pressure by exchanging heat with outdoor air. After that, the liquid-phase refrigerant of high-temperature and high-pressure sent from the condenser 2 rapidly expands by a throttling action of the expansion valve 3 and is sent to the evaporator 4 in a wet-saturated state of low-temperature and low-pressure. The evaporator 4 exchanges heat between the refrigerant and air blown to the interior of the vehicle by a blower (not shown). Then, the refrigerant is evaporated in the evaporator 4 and discharged in a gaseous phase of low-temperature and low-pressure. After that, the vapor-phase refrigerant is inhaled into the compressor 1, and then, recirculates the refrigeration cycle as described above.
The evaporator is mounted inside the air-conditioning case mounted to the interior of the vehicle to cool the interior of the vehicle. That is, the air blown by the blower (not shown) is cooled by evaporative latent heat of the liquid-phase refrigerant circulating inside the evaporator 4 and discharged to the interior of the vehicle in a cooled state so as to cool the interior of the vehicle.
Moreover, the interior of the vehicle is heated by a heater core (not shown), which is mounted inside the air-conditioning case, and, through which coolant of the engine circulates, or by an electric heater (not shown) mounted inside the air-conditioning case.
In the meantime, the condenser 2 is mounted at the front side of the vehicle to radiate heat while exchanging heat with air.
Recently, an air conditioning system which carries out heating and cooling only using a refrigeration cycle has been developed. As shown in FIG. 2, such an air conditioning system includes: a cold air passageway 11 and a warm air passageway 12 which are partitioned to the right and the left inside a first air conditioning unit 10; an evaporator 4 mounted on the cold air passageway 11 for cooling; and a condenser 2 mounted on the warm air passageway 12 for heating.
In this instance, at an outlet of the air conditioning unit 10, air outflow ports 15 for supplying air to the interior of the vehicle and air discharge ports 16 for discharging air to the exterior of the vehicle.
Furthermore, blowers 20 which are operated individually are respectively mounted at an inlet of the cold air passageway 11 and at an inlet of the warm air passageway 12.
Because the warm air passageway 12 and the cold air passageway 11 are arranged at right and left sides (in the width direction of the vehicle), the two blowers 20 are also arranged at right and left sides.
Therefore, in a cooling mode, cold air cooled while passing through the evaporator 4 of the cold air passageway 11 is discharged to the interior of the vehicle through the air outflow ports 15 to cool the interior of the vehicle, and in this instance, warm air heated while passing through the condenser 2 of the warm air passageway 12 is discharged to the exterior of the vehicle through the air discharge ports 16.
In a heating mode, warm air heated while passing through the condenser 2 of the warm air passageway 12 is discharged to the interior of the vehicle through the air outflow ports 15 to heat the interior of the vehicle, and in this instance, cold air cooled while passing through the evaporator 4 of the cold air passageway 11 is discharged to the exterior of the vehicle through the air discharge ports 16.
In a dehumidification mode, the air conditioning system is operated like in the cooling mode so that dried cold air passing the evaporator 4 is supplied to the interior of the vehicle to cool and dehumidify the interior of the vehicle.
Moreover, in the conventional air conditioning system, the evaporator 4 and the condenser 2 are arranged inside the first air conditioning unit 10 and a compressor 1 and an expansion valve 3 is arranged outside the air conditioning unit, so that the evaporator 4 and the condenser 2 are connected with the compressor 1 and the expansion valve 3 through a refrigerant line L.
The first air conditioning unit 10 supplies air-conditioned air to the front seat space inside the vehicle, and as shown in FIG. 2, the second air conditioning unit 50 is mounted in order to supply air-conditioned air to the rear seat space inside the vehicle.
The second air conditioning unit 50 includes a rear evaporator 51 and an electric heater 52, and the rear evaporator 51 is connected with the refrigerant line L of the first air conditioning unit 10 through a rear refrigerant line L1.
Furthermore, an expansion valve 53 for expanding refrigerant supplied to the rear evaporator 51 is mounted on the rear refrigerant line L1.
Therefore, in a single cooling mode that only the first air conditioning unit 10 is operated, the expansion valve 53 is closed so that refrigerant does not flow to the second air conditioning unit 50, but in a dual cooling mode that the first air conditioning unit 10 and the second air conditioning unit 50 are all operated, the expansion valve 53 is opened so that expanded refrigerant flows to the second air conditioning unit 50.
Additionally, in a single heating mode and a dual heating mode, the expansion valve 53 is closed so that refrigerant does not flow to the second air conditioning unit 50.
However, because the expansion valve 53 is closed in the single cooling mode that only the first air conditioning unit 10 is operated, the conventional air conditioning system has several disadvantages in that an oil circulation ratio which has influence on durability of the compressor 1 is reduced since oil remaining in the rear refrigerant line L1 of the second air conditioning unit 50 is not circulated, and in that discharged pressure of the compressor 1 rises since a flow of refrigerant to the rear refrigerant line L1 of the second air conditioning unit 50 is blocked.
In addition, the expansion valve 53 must be closed in the dual heating mode that the first air conditioning unit 10 and the second air conditioning unit 50 are all operated, but the expansion valve 53 is often opened automatically when indoor air is introduced into the second air conditioning unit 50 and temperature of an outlet of the rear evaporator 51 rises. So, in the dual heating mode, the expansion valve 53 of the rear refrigerant line L1 is operated and expanded refrigerant is supplied to the rear evaporator 51 of the second air conditioning unit 50, and it causes deterioration in heating performance using the electric heater 52 inside the second air conditioning unit 50.